First time sewing, need help!

Samantha

I bought my first sewing machine and planned to make some things before baby gets here. Burp cloths seemed simple enough, it just said to sew 2 pieces together, flip so it's not inside out and then sew a border around.

My question is, after I flip it, how do I get the part that was left open to look like it blends in? I tried the other day and the edge was slightly frayed and you could definitely see it😐